According to the Standard Model of particles and forces, the Higgs mechanism gives mass to elementary particles such as electrons and quarks. Its discovery would answer one of the big questions in physics: What is the origin of mass?

Scientists from the CDF and DZero collaborations at DOE's Fermilab have combined Tevatron data from their two experiments to increase sensitivity for their search for the Higgs boson. While no Higgs boson has been found yet, the results announced today exclude a mass for the Higgs of 170 GeV/c2 with 95 percent probability (see graphs). This is the first time that the Tevatron experiments directly restrict the Higgs mass. Earlier experiments at the Large Electron-Positron Collider at CERN excluded a Higgs boson with a mass of less than 114 GeV/c2 at 95 percent probability. The results show that CDF and DZero are sensitive to potential Higgs signals. The Fermilab experimenters will test more and more of the available mass range for the Higgs as their experiments record more collision data and as they continue to refine their experimental analyses. The expected exclusion limit (red-dotted line with green and yellow bands in lower graph) will move up as the two collaborations collect and analyze more data.

The Fermilab accelerator complex accelerates protons and antiprotons close to the speed of light. The Tevatron produces millions of proton-antiproton collisions per second, maximizing the chance for discovery. Two experiments, DZero and CDF, search for new types of particles emerging from the collisions.

The CDF detector, about the size of a 3-story house, weighs about 6,000 tons. Its subsystems record the "debris" emerging from each high-energy proton-antiproton collision produced by the Tevatron. The detector records the path, energy and charge of the particles emerging from the collisions. This information can be used to look for particles emerging from the decay of a short-lived Higgs particle.

The DZero detector records particles emerging from high-energy proton-antiproton collisions produced by the Tevatron. Tracing the particles back to the center of the collision, scientists understand the subatomic processes that take place at the core of proton-antiproton collisions. Scientists search for the tiny fraction of collisions that might have produced a Higgs boson.